Confusion has existed as to what sand reclamation means, particularly in the early years of sand conditioning. Some foundrymen deemed reuse of old used sand a form of reclamation, while others deemed rejuvenation of old sand heaps with new sand and clay additions to be reclamation. Yet others felt that the mechanical reconditioning of an old sand mass by merely removing lumps, foreign metal and ultra fine particles, should be accepted as reclamation. Only a few in the earlier years conceived reclamation to be a matter of treating individual grains to restore them to a physical state approximating that of new sand grains. It is this latter meaning that applies in this disclosure because it has become the accepted meaning of sand reclamation in modern foundry technology. One recent twist may be added to this definition: it should include the reclamation of new sand which is below ground mined; although it is new sand, it contains quantities of impurities which must be removed if they are to be equivalent to bank sand or above ground mined sand.
Sand reclamation has been slow in being accepted by the foundry for commercial implementation. There has existed for some time an industrywide attitude that reclamation only adds to the complexities of selecting, preparing, testing and controlling the sand to be used to make cores or molds. The average foundryman is adverse to changing established procedures that have taken years of trial and error to arrive at the right binder chemistry, shape, flowability, and grain size that will give the right ramming pressure and carrying properties. Reclaim sand is believed, in accordance with this attitude, to introduce additional unknown variable and technical considerations that trade off new problems for solving the immediate problem of conserving sand. This invention is designed to provide a reclaim sand product that does not trade off new problems; the reclaim sand is defined by a number of parameters that make it substantially the same as new bank sand and in many cases better.
The primary consideration that has guided the course of sand reclamation development heretofore has been the technical success of the particular process in terms of the quality of the reclaim sand; today the important considerations are (a) the cost of energy employed in the process, (b) the amount of land that is required to support the processing equipment, (c) governmental regulations of waste disposal, and (d) density or chemical variability of the reclaim sand preventing sand bonding for core making.
The progression of the technology includes reuse of old sand, rejuvenation by dilution, reconditioning, wet methods, thermal methods, dry methods, and combination of the latter. With this in mind, a review of the fundamental concepts for each of these categories shall follow: